1. Field of the Invention
The present invention relates to an image data processing method and an apparatus therefor, for inputting image patterns, such as figures, in the form of vector data to obtain image recording data suitable for recording through sequential scanning.
2. Description of the Prior Art
Well known in the art is an apparatus for recording image patterns inputted from a CAD or the like on a photographic film or printing paper using a sequential scanning/recording system such as a process scanner or a printed circuit pattern recorder. Such image patterns include figues, designs and/or characters. In such an apparatus, data on segments forming respective figure patterns or the like are inputted regardless of sequence along the scanning direction, and hence a function of permuting the inputted patterns along the scanning direction is required.
Such permutation (sorting) of the segments has been generally performed through software processing. However, such a sorting process is executed through comparison processing, and hence the same is not suitable for a computer which is principally designed to perform various calculations at a high speed rather than comparison processing. Therefore, utilization efficiency of the apparatus is reduced when the sorting processing is performed by software manner. Further, software processing does not satisfy the requirement for high speed processing.
In order to perform sorting using hardware, on the other hand, a memory having a recording capacity responsive to the pixel number of the recording plane is prepared. Segment data forming respective unit patterns are written in the memory with recording coordinates thereof being processed as addresses, and then the respective segment data are read in sequence of scanning. In this case, however, a memory of extremely large storage capacity is required.
Consider a case of performing sorting processing on three segments L.sub.1 to L.sub.3 as shown in FIG. 1A, for example, where circles, squares and triangles denote pixels forming the segments L.sub.1 to L.sub.3 respectively. In order to sort these segments, a memory having capacity for the entire pixels (8.times.8 =64 pixels in FIG. 1A) forming the recording plane must be prepared as shown in FIG. 1B. Although the illustrated pixel number is small since FIGS. 1A and 1B are schematic diagrams, an extremely large memory capacity is required in practice. For example, in the recording of the circuit pattern for manufacturing a printed circuit board, the memory capacity amounts to 2.sup.18 .times.2.sup.18 =64 gigabits for manufacturing a print pattern of 1m.times.1m through pixels of 5 .mu.m.times.5 .mu.l m each.
With such an increase of the memory capacity, further, empty data such as those shown by "--" in FIG. 1B are also accessed when the data are read from the memory in sequence of scanning, whereby memory access time is also increased. Therefore, the total time for data reading is lengthened to slow the processing. When as a result the reading speed cannot keep up with the recording speed, output data must be temporarily stored in a high-speed memory device for read out to a recording apparatus. However, employment of such high-speed memory device leads to an increase in cost.
In order to cope with this, introduced is a concept of "classification memory", which is a memory having capacity for several lines with respect to the subscanning direction, as shown by S.sub.1, S.sub.2, . . . in FIG. 2. A plurality of such classification memories are prepared to be alternately utilized, thereby to roughly perform sorting in the subscanning direction. Then obtained are data per recording pixel required for recording in the main scanning direction. Such data are written in addresses corresponding to the recording positions in a memory having a capacity identical to the recording pixel number in the main scanning direction. Sorting is also performed at this time. Then data are read in sequence of addresses, to perform image recording. However, such sorting for recording is mainly directed to the case of recording characters or the like on a relatively small recording plane, and hence the same is on the premise that the memory capacity required for one line is small, 2.sup.16 bits, for example.
Therefore, when such a sorting process through the memory for main scanning/recording is applied to image recording directed to a wide region such as the print pattern of a printed board, a capacity amounting to 2.sup.18 bits is required for one line, leading to an increase in memory capacity. When an output device is a multi-channel one having 10 channels, for example, parallel recording for 10 lines is performed in one scanning operation. In order to perform such parallel processing, there are required a memory capacity ten times that of the case of a monochannel device as well as ten memory reading processing units, whereby the apparatus is further increased in size. When such recording is performed through one memory reading unit, data for ten lines may be read in series in one scanning interval. In this case, however, a memory of a high reading speed is required; such a high-speed memory however is expensive.
Thus, an important subject of such an apparatus is to reduce the memory capacity and increase the processing speed in recording on large image plane.